This project has initiated an investigation of the intracellular biological functions of the various alpha-mannosidases in eukaryotic cells, using Saccharomyces cerevisiae as a model system. A particulate enzyme has been isolated which attacks a variety of mannose containing substrates. The enzyme appears to be a glycoprotein with a molecular weight of 400,000 daltons. The enzyme is regulated by catabolite repression and increases 8-fold during sporulation. This increase during sporulation is blocked by the addition of ammonium ions to sporulation medium. The enzyme was found to localize inside the vacuole of the yeast cell. A number of mutations of this enzyme have been isolated and are currently being investigated.